Motorcycle Forum banner

1 - 20 of 34 Posts

·
Registered
Joined
·
26 Posts
Discussion Starter #1 (Edited)
I own a 2 stroke 150 sportbike. The braking power is impressive if done correctly. However i noticed there were times when I used front brake only - hard. It would cause the rear wheel to slide left or right.

1) Once when lane splitting in a traffic jam. I was going abt 30km/h & i slipped into lane when i found a gap. A while later i decided to lane split again, chked back & found a motorcycle approaching so i didnt move out. But when I turnd my head back to the front I realised traffic had stopped & I was just abt 2 meters behind the back of a cab! I instinctively I jammed the front brake & the rear just slid left until the bike was parallel to the rear of the cab. Luckily no accident, but the whole throw of the rear also threw me forward & I smashed my nuts against my fuel tank.

2) Out with a riding buddy. Going at abt 50 km/h. I thought he would be going straight but he signalled late & turned right. I braked hard to slow down to make the right turn & rear wheel slid left a little.

3)another occassion with that buddy on a narrow twisty rural road. Going abt 50km/h. On a particular tight left bend I noticed i was going wide so I used front brake to reduce speed to get back on line, the rear wheel slid a little to the right.

My buddy theorises that my front braking was hard enough to cause a very slight lift of the rear wheel => loss of traction => slide. Is this correct or is there something wrong with my rear suspension? During my e-brake lessons, too much rear brake causes the rear tyre to slide (fishtail)

or is it the case where front wheel speed has slowed down much faster then rear wheel. rear wheel has nowhere to go hence it throws to the side? Sorta like a steel member in bending - top fibres in compression, bottom fibres in tension. Top fibres compress until it has no place to go hence it throws to the side & away causing lateral torsional buckling of the member.

However if i use both brakes, rear wheel slide never happens.

Im an engineer btw.
 

·
Gone
Joined
·
23,907 Posts
I'm not really sure with what's going on there with the rear wheel. It could be any of those you mentioned above.

Three things to consider before you end up having something worse happen:

1) Increase the time and space around you when you are riding. It sounds like you are getting very close to the limit of what you and your motorcycle can handle. If you misjudge even a little at this point, it could mean a crash. Leave yourself enough reserve in space and time so you won't have to brake hard.

2) Look further ahead and work on being able to predict potential problems before they become an issue. Suspecting a possible trap and reacting to it early will make it an non-issue.

3) Practice your quick stop skills until you can use them without thinking about them. Learn to progressively use the brakes rather than just grabbing them. Use both brakes effectively. Your stops will get shorter and be under control with practice.

I'm not trying to be critical here, just throwing out some tips that hopefully will keep you up on two wheels.
 

·
American Legion Rider
Joined
·
23,527 Posts
Wild though only here. Is it possible your bike has linked brakes and they are grossly out of adjustment? I've never had the rear end kick out and I've put the binders on hard. In you first example you was going straight so there should not have been a reason to kick out. Does sound like you need to add space. I get after my wife for traveling to close but she has a depth of field issue.
 

·
Pale Rider
Joined
·
528 Posts
I always lead with the rear brake. Why? Because when I lead with the front brake, the nose dives, offloading the rear tire, destabilizing the entire bike -- and whoever is riding it. When I lead with the rear brake, the nose dive is small, or eliminated entirely, and the suspension, front to back, is more stable.

Also, the rear brake supplies 30% of the stopping power, and I want all of it! Every last percentile... I'm very greedy that way. ;)

Go to a parking lot, and practice leading with the rear brake. Then try the same speed, and same stop, with just the front brake, but be prepared! Play with the techniques, at different, SAFE, speeds, from 15 KPH, to 40 KPH. The key is to train your brain to use both brakes, preferably with a slight lead on applying the rear brake, just ahead of engaging the front brake, in all situations. Be smooth, and strong, but do NOT grab either brake!

Make certain your tires have sufficient tread left on them. When they wear down to the bars, it is time for new skins -- don't be cheap! It's your life depending upon those two tires... Tires which last fewer miles, tend to be softer rubber which grips the road much better; harder tires achieve more miles before wearing to the bars, but they tend to have less traction, and slide easier. I sacrifice mileage for traction, achieving only 12k out of my rear tire of choice, but it glues my heavy touring bike, with my bride on board with me, to the roadway, wet or dry. They're worth every penny to me, even though I could put touring tires on, and get 20k miles out of a rear tire. I consider them money well spent. Cheers!
:coffee:
 

·
Gone
Joined
·
23,907 Posts
If the rear wheel lifts up during a quick stop, it may tend to slide sideways since there may still be some momentum as the front wheel comes to a stop.
 

·
Registered
Joined
·
68 Posts
Your buddy is entirely correct, that's why you're supposed to use BOTH brakes on hard braking, or any braking for that matter.
 

·
Premium Member
Joined
·
5,640 Posts
You'll get the same effect with a front-drive car with manual transmission on wet pavement - the rear will come around on you if the braking on the front is too much greater than the rear. The rear unloads and loses grip, but is still trying to go as fast as before the front brake was applied, and even the slightest tilt to one side will make it go around. Controlling a 'stoppie' the way they do in the movies is a lot harder than just slamming the front brake, which is why it makes for a cool effect that few can master.
 

·
Registered
Joined
·
2,637 Posts
If the rear wheel lifts up during a quick stop, it may tend to slide sideways since there may still be some momentum as the front wheel comes to a stop.
This sounds like the problem to me as well. Plus it seems you're riding way to close and aggressive.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #9 (Edited)
Hi everyone! Thanks so much for your inputs & replies :) Thanks too for confirming my buddy's theory! Most appreciated. :) I'll try to improve on my quick stop techniques

@hogcowboy - nope. No linked brakes.

@sgtslag - During my learning period we learnt to use both brakes simultaneously. For some reason or other, since last week i think, I noticed ive started using rear brake 1st, for 1-2 secs & then follow it with front brake. The stopping at junctions & lights does seem much smoother.

With regards to the rear tyre, I bought the bike 2nd hand. I did notice that the rear tyre was more worn then the front. However it still passed my mandatory annual vehicle inspection last weekend, applicable for all vehicles > 10 yrs old. I did read in some forum that tyre compounds get harder with age, hence reduction in grip. P'haps that too contributed in part to my sliding problems. I think I will go & change the rear tyre soon rather then wait for it to reach the legal wear limit.
 

·
Gone
Joined
·
23,907 Posts
It's a good idea to change tires before they get too old. Depending on how much sun and elements they are exposed to, 5 years is probably as far as you want them to go.
 

·
MODERATOR
Joined
·
8,572 Posts
Weight transfer to the front end unloads the rear weight and can cause a skid of the rear wheel during heavy braking. Ever wonder why some/ few or most rear brakes are barely sufficient to easily lock the rear wheel? The bike is engineered that way to avoid easy rear wheel slides which are very dangerous. The common response by the inexperience during a panic stop is to stomp on the rear brake;)

Sam:coffeescreen:
 

·
American Legion Rider
Joined
·
23,527 Posts
I've never had that problem of rear unloading and I seldom use the rear brake. That's for emergencies. I wonder if my lack of seeing that is because of the pig I ride(heavier). But I never had the problem on the Hawk either but 90% of the time I was 2 up on it.

Just wondering if the weight difference on the hog comes close to the added weight of the Hawk. Or is the real problem with those that don't have a feel for where their maximum braking is for their bike. Every bike I've ever had I have tested the brakes until I knew what they did. My point is, either it's the weight or it's understand your particular brakes.

I'm thinking it's not understanding your brakes. Like it's the last thing to worry about. So it gets completely forgotten about. Does that make sense?

Everyone is worried about the go part and forget about the stop part when practicing. Guess I'm a chicken because I check the brakes first.

We've got some folks with new to them bikes. Did y'all just test the throttle or did you test the brakes too? Just curious.
 

·
Retired twice: Navy and as a govt contractor
Joined
·
14,300 Posts
When I first got this bike during hard braking I was unloading and dragging the rear tire. I had been hitting it first, semi-hard and when I applied a lot of front brake it took all the weight off the rear.

Practiced and practiced with the same result - until - I tried applying the front brake first and then I could hit the rear as hard as I needed.
 

·
ZAMM Fanatic
Joined
·
2,730 Posts
I'm gonna concur with the others and blame your apparently light rear end on weight shift.

(if we could patent that phenomena & sell it on TV ..."Want a lighter rear end? Don't lose weight, just SHIFT IT to more desirable locations!" we'd BE RICH!

now headed slightly off topic... still about weight shift though...

1974, Triumph TR-3 (car), tended to understeer a little bit... so I'm coming around a perfect S-turn 3-5mph faster than the time before but the front end is pushing...right into the other lane where another car is headed directly towards my path of motion..... I'm thinking explaining a head-on to my Dad is NOT going to go well...

Novice driver that I am, I jam the brakes.

The nose dives, the weight transfers to the front, the front tires hook up, and now that they've got adequate traction (I'd been countersteering) the car dives right over the curb and into a guy's brick mailbox.

Only about the 12th time that year his mailbox had gotten nailed, fwiw. Cost me a whopping $80 in 1974 dollars to get it rebuilt. ...Rumor was he was getting volume discounts from the local mason...

So weight shift under braking can work for you or against you.... what I hear being discussed on MC forums is "trail braking" into a corner, that is, pre-applying SOME brake to compress the suspension even if you don't need to slow down to make the corner. For improved cornering performance.

Never really heard whether "trail braking" is supposed to be performed using the front, front & rear, or rear brake only.
 

·
Subversive
Joined
·
416 Posts
I think some bikes are prone to lifting the rear.. Even on my GS550 the rear never felt like it was going to unload... On that bike I used the rear more so than on my current heavier bike....

In pro racing you see the rears come up a lot so I'm not sure what to infer from that...
 

·
Registered
Joined
·
4,168 Posts
If you are using all available braking from the front and have a short wheelbase, you may indeed be pushing hard enough for the rear to lose most or all of its traction. I drive a very long wheelbase bike and can no way get that effect but look at your bike as just so many centers of mass and so many points that provide stopping power. When x amount of stopping force acts at a point that is very low and at the front of the bike, what happens to the rest of your equations? Does the rotational force of that braking cause the bike's weight to be reduced to less than its real vertical weight? That means the rear will come off the ground. In that case you have lifted the rear wheel and it has no traction at all. It all comes down to how effective the brakes are at stopping that front wheel compared to how much weight transfer takes place. On a long wheelbase bike, the weight will never transfer far enough for that to happen but on shorter wheel bases that is not the case.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #17
Never really heard whether "trail braking" is supposed to be performed using the front, front & rear, or rear brake only.
Trail braking is front brake. Something to do abt maintaining some front brake pressure as you enter the turn & gradually decreasing as you go through the turn & completely releasing it just before exit getting on the throttle again. Something like that. Others, please correct me if im wrong here.

If you are using all available braking from the front and have a short wheelbase, you may indeed be pushing hard enough for the rear to lose most or all of its traction. I drive a very long wheelbase bike and can no way get that effect but look at your bike as just so many centers of mass and so many points that provide stopping power. When x amount of stopping force acts at a point that is very low and at the front of the bike, what happens to the rest of your equations? Does the rotational force of that braking cause the bike's weight to be reduced to less than its real vertical weight? That means the rear will come off the ground. In that case you have lifted the rear wheel and it has no traction at all. It all comes down to how effective the brakes are at stopping that front wheel compared to how much weight transfer takes place. On a long wheelbase bike, the weight will never transfer far enough for that to happen but on shorter wheel bases that is not the case.
Wheelbase is the distance between the wheels is it? According to the specs its 1330mm. So is that considered small? It is a small sportbike anyway.
 

·
American Legion Rider
Joined
·
23,527 Posts
Mine is 1612.9mm and I think it's too short.:)
 

·
Registered
Joined
·
4,168 Posts
My wheelbase is listed as 1670 mm. Yes, that is longer than even the average touring bike. No way I can lift my rear wheel. The front wheel would be sliding first. With ABS my front wheel never can slide so I always get some, sometimes not much, braking from my rear wheel. According to HD their Road Glide wheelbase, the most tour worthy of the HDs, is a mere 1625mm. Yes my bike is quite long.
 

·
Retired twice: Navy and as a govt contractor
Joined
·
14,300 Posts
Made me curious so I had to look, 1715 mm. No wonder I can't turn around in a 24' circle.
 
1 - 20 of 34 Posts
Top